Compass checking device



y 1950 o. RASMUSSEN 2,507,933

COMPASS CHECKING DEVICE Filed Feb. 26, 1949 a-7 I 2 a I l/Y YEN 79k 044/fS/WUSSf/Y Patented May 16 1953 UNITED STATES PATENT OFFICE 2,507,933COIWPASS CHECKING DEVICE Olaf Rasmussen, Port Clinton, Ohio ApplicationFebruary 26, 1949, Serial N 0. 78,531

6 Claims.

This invention relates to an improved device for checking the accuracyof compasses. 3 It is among the objects of the present invention toprovide a simple and reliable device for checking compasses particularlyof the type used by marines.

A further object of the present invention is to provide a compasschecking device adapted not only to use sunlight as a means forproviding checking indications but also adapted to use a prevailing windfor the same purpose in case the sunlight is not available.

Further objects and advantages of the present invention will be apparentfrom the following description, reference being had to the accompanyingdrawings, wherein a preferred embodiment of the present invention isclearly shown.

In the drawings:

Fig. 1 is a perspective view of the improved compass checking device.

Fig. 2 is a fragmentary sectional view of the device.

Fig. 3 is a detail view of the friction providing elements of thedevice. The present invention provides a reliable, accurate and simplecompass checking device which may be produced commercially at a minimumcost of time and material, therefore making available low cost equipmentfor operators of small pleasure cruisers. By having the device of thepresent invention available, the small boat owner may check his compassfrom time to time and particularly when an extended cruise isanticipated even though his compass has previously been compensated by acompetent person. Because of shifting of metallic objectson board theboat or for various other reasons, a previously compensated compass maybe rendered inaccurate and by testing it with the device of the presentinvention such inaccuracies may readily be discovered and correctionsmade.

Referring to the drawings, the numeral designates the base plate, whichis provided with spaced suction cups 2| by means of which the device maysecurely be attached to any suitable stationary member on the boat,preferably in close proximity to the compass. Base 20 is preferablyround and has a central opening 22. A centrally apertured spacing collar23 is centrally secured to the base plate on the side opposite thesuction cups.

A dial 25 having a central aperture is rotatably supported upon thespacer collar 23, pin 26, extending through the central apertures of thedial 25, collar 23 and base 20, holding these members coaxial. Pin 26has an enlarged head portion 21 providing an annular flange 28 whichengages 70. Spring 29 is biased toward the base and a pin 30, extendingtransversely through pin 26, provides an abutment for the biased spring29 so that it constantly exerts a pull upon the pin 26 whereby theflange 28 of its head frictionally engages the dial and constantly butyieldably resists its rotation relatively to the base.

Dial 25 is disc-shaped and has a plurality of radially arranged vanesextending at right angles from the side thereof opposite the base. Thesevanes are equally spaced one from the other. Fig. 1 shows the dial 20 ashaving eight, comparatively thin, triangularly shaped vanes or fins 32,33, 34, 35, 3B, 31, 38 and 39 respectively. Each fin extends radiallyfrom the outer edge of the dial, stands at right angles to the outerface of the dial and is at 45 angular relation to the next adjacentvane. Alternate fins or those numbered by the even numbers in Fig. 1 arelarger than the intermediate fins or those numbered by the unevennumbers. They may be attached to the dial in any suitable manner, thepresent drawings showing each having a tang 40 which fits into a radialslot in the dial. The tang may be welded or peened over to fasten thefin securely to the dial.

The head 21 of pin 26 has an axial recess 4| into which a post 42rotatably fits. Post 42 has a weathervane 43 radially extendingtherefrom so that relative rotation between the post 42 and dial 25brings the weathervane into vertical alignment with the respective fins32 to 38 on said dial.

The device of the present invention is used in the following manner; tocheck the compass, the navigator of the boat stops his boat incomparatively open waters and heads it in a selected direction, as forexample, nort as indicated by the boat's compass. The compass checkingdevice having been secured to a suitable stationary part of the boatfully exposed to sunlight is then initially adjusted by turning the dial25 relatively to the anchored base 20 until the specially marked fin,the one numbered 34 in Fig. 1 and marked X, casts a sharp, narrow shadowon the base 20 which is preferably finished in a light color moreclearly to show the shadow. All other fins, excepting the onediametrically opposite the one marked X, cast triangularly shapedshadows as shown in Fig. 1. The checking device is now set and remainsuntouched for the remaining portion of the test.

After so setting the checking device, the boat is slowly turned, on itsvertical axis, completely around until the compass again indicatesnorth. As the shadow cast upon the base 20 by each successive finbecomes distinctly narrow and sharp, the navigator checks the degreesindicated on the compass rose. If, as each fin shadow becomes narrow andsharp, the compass rose does not indicate a 45 shift, then the navigatorknows the compass is not functioning precisely. The amount of deviationby the compass may readil be discerned as each fin casts its narrowestand sharpest shadow which, if the compass is functioning precisely, willindicate 45 intervals on its rose or dial, however, if the compass isfaulty, the difference plus or minus may immediately be ascertained. Thecompass, may then properly be adjusted or compensation for the knowndeviation be made during a-cruise- Bright sunlight may not always beavailable when it is found necessary or desirable to "testthe compassand therefore :the, aforedeecribed process for testing would not bepossible. I-lqwever, the device of the ,present invention 'isnot limitedsolely to the use of sunlight for testing purposes "On the contrary,ifisunlight is not. available, wind .m'ay be used forthesame purpose.

Generally a steady or prevailing vbreeze or wind is; found aboutsubstantially open :waters. Due to the simplicity of the device"checking should require no more than ten :minutesand usually .a steadyand prevailing breezeor wind with .a velocity ofeat. least 1 to 2.:milesper hour is :available.

.For testing by wind, the post =42 with its weather-vane 43 1s attachedto. the checking-device :by inserting the post into the-recess "4i. Asbefore, the boat. is headed directly north accord-. ing to the compass.The wind striking the vane 3, .will move it.:into a definite positionand "main, tainlitthere. Now .the 'dialis rotated'until the vane Unis inverticalalignment with the fin34, marked X as shown in Fig.1.Followingthis the. boat is slowly'turned onits vertical axisand as=each::fin, being rotated with the boatpvertically: aligns with'the vane43, thecompass, if true. should indicate a 45 turningmovement of theboat. As with the sunlight process, if the compass is inaccurate, itwill indicate a turn of more or less than45 between'therespectivealignment of "the vane With the finsand thus the-degree of inaccuracymay be established in each 45 sector.

From the aforegoing description i it may be seen that the device'of thepresent'invention is exceedingly simple and inexpensive, yetaccurate anddependable. It may be usedinbright sunlight for checking the compass or,if;sunlight {1S not available, a usually existing breeze or wind of atleast 1 to z'mil'es per hour may lac-use instead. :Aireliable check .onthe accuracy of'thc I 'compess may 'bemade by'this, device inpractically all kinds of weatheiyeither'brighter oven. cast and dull and'theoperation mavbe com, pleted .in a relatively short time.

While the embodiment ofthe present invention as herein disclosed,constitutes-a preferredform, it is to be understood that other formsmight be adopted, all coming within -the rscope :of'the claimswhich'follow.

What is 'claimedls as follows:

-1. In a compass checking device-thecombination with a base providedwithimeans ffor removably attaching said base to an immovable :mem 'beradjacent the compass to be checked; of a dial rotatably mounted upon thebase; 'means interposed betweenithezplate and dial,-saidmeans engaging"oothplateand dial and being operative frictionally'to resist rotationof the dial; a plurality of fins extending at right angles from thesurface of the dialopposite the base, said :fins being radially spacedat-45 degrees one from the other.

2. In a compass checking device'the combination with a basehavingacentral aperture;.suction cups secured to; one side of the base for at-4 taching the base to an immovable object adjacent the compass beingcheclged a centrally apertured; dial; a pin extending through theapertures of'the base and dial said pinhaving an enlarged head engagingthe dial, and rotatably se- "curing the dial on the base; a spacercollar between the base and dial; resilient means interposed between thepin and base, urging the head ofthepin upon the dial for frictionallyresisting right angles from the side of the dial opposite the base, andbeing equally angularly spaced one relatively to the other.

3. In a compass checking device, the, combina: tion with a stationarybase; of a dial 'rotatablv mounted .uponsaid base; frictional m ans.hitch posed between the dial and base, said. means be: ing operativeyieldably to resist rotationof dial; aphiralityof radially arranged finsextending at right anglesfrom theside ofthe dial on: posite the basasaidfins :being egually, angulgflg spaced; a vertical post attachable to thedial axially thereof and rotatable relatively'theretq; and aweather-cock in the form. 0.? a (81 ext nd ing radially fromthepost.

4. A device as defined by-claim'Z in which, howevcrytheipin has, anaxial recess in its h dv edsen'd; apost 'rotatably-fitting into saidrecess; and;a weather vane extending vradia l Qm 3 post and over therespective disoevanes.

.5. Aidevice for checking a compass s c red' a boat, comprising incombination, a-base having means forattaching it toan imm vabl p rt' theboat adjacent the compass; a dial carried by the :base :and having apluralityof secured thereto and equiangularly-spaced one-relae tivelyLtd the other, each fin being S0, s ape 4 45 to successively cast acomparatively narrow and sharprlinezshadow on the dial when broughtintoa predetermined position relatively to the sun as the 'boat is :turnedcompletely around on its vertical axis; and a rotatable weather-vaneaxle ally supported on theidial-and movable Successive,- lyintoverticalalignment'withzthe said members on the :dial, .by-a prevailing wind asthe boatzis turnednompletelyaround on said axis. 6. "In acompasscheckingdevice, the combine.- tion witha:stationarybase; .anindicating digl mounted upon the'baseso as to be grasped and itselfrotated: in either directionrelati-vely there: to; frictional meansinterposed between the base and-:dial, said means'yieldably resistingrotation of the dial on the base and holding said dial in any rotatablyadjusted position onsaidibase; and a plurality-of :completely fiat,'wflfelelikg fins extending edgewise from the side of 'thedialope positethe base andta'djacent theperipheral edge of the dial, 'eachzfin havingits entire fiat surfaces arrangedcdiametrically of the dial, all finsbeing at right an'gles'to the face of the dial and eguali 'space'donefrom' the other.

OLAF RAsMUss n,

REFERENCES CITED

